Change in body mass index (BMI) does not reflect body composition of patients undergoing treatment for acute lymphoblastic leukemia (ALL). This study, published in Leukemia & Lymphoma, suggests direct measures of body composition should be used to evaluate obesity in patients with leukemia.1

This study found the discrepancy between BMI and body composition is due to increases in body fat with simultaneous loss of lean muscle mass during treatment. The research was conducted by an interdisciplinary research team at The Saban Research Institute of Children’s Hospital Los Angeles (CHLA). Previous work has found that obese children with high-risk ALL had a 50% greater risk of their disease recurring compared with children who were not obese. ALL is the most common childhood cancer.

“In my lab we’ve seen a direct interaction between fat cells and leukemia cells that may help explain this increased risk of disease relapse,” said senior author Steven Mittelman, MD, PhD, director of the Diabetes and Obesity program at CHLA. “It appears that the fat cells protect leukemia cells, making them less susceptible to chemotherapy, and making an accurate measure of body fat essential.” Mittelman is also an associate professor of Pediatrics and Physiology and Biophysics at the Keck School of Medicine of University of Southern California.

BMI, which is calculated from height and weight measurements, is typically used to estimate body fat and determine obesity. However, it does not differentiate between fat and muscle tissue. Thus, BMI may be unchanged when body fat increases and lean muscle is lost concurrently, making body composition estimates based on BMI inaccurate.

This study prospectively enrolled 50 patients, who were predominantly Hispanic, age 10 to 21 years, and with newly diagnosed high-risk B-precursor ALL or T-cell ALL. The gold standard of dual-energy x-ray absorptiometry (DXA) was used to measure percentage of total body fat and lean muscle mass. These were measured at time of diagnosis, 1 month later, and later during chemotherapy treatment. In addition, the researchers determined BMI z-score at each time point, which is a measure of how a given child’s BMI deviates from a population of children of the same age and sex.

“We found that change in BMI did not reflect changes in body fat or obesity,” said Etan Orgel, MD, an attending physician in the Survivorship & Supportive Care Program at the Children’s Center for Cancer and Blood Diseases at CHLA, and first author of the study. “In some patients, reaching a healthy BMI was due solely to loss of muscle even while body fat continued to rise. Based on these results, we believe that evaluation of obesity in patients with leukemia should include direct measures of body composition.”